It is known that the traditional rotating machines are subjected to vibrations during their functioning.
Said vibrations originate from multiple causes, many of them to be related to a non-optimal balancing of the parts in motion of the rotating machines that, during the movement, changes into a force variable in time that induces the machine itself to vibrate.
Even if light vibrations of the rotating machines can be tolerated in particular non-critical environments, there are also multiple applications wherein said rotating machines cannot vibrate, or must maintain their vibration to extremely reduced levels in any operating conditions, at low and high charge, and on a rather wide rotation speed interval.
Particularly—but not necessarily—in aeronautical applications and on aircrafts in detail, rotating machines (typically jet engines) that require a particular care for what concerns the reduction of vibrations are used. As a matter of fact, the vibrations produced by a rotating machine can induce vibrations to all the parts of the aircraft and therefore indirectly also within the nacelle.
The vibrations of a rotating machine can have a fixed frequency or a frequency that varies with the variation of the rotation speed of the machine itself, as well as they can increase or diminish in their intensity on the component in fundamental frequency and/or on the harmonics as a consequence for example of charge transients imposed to the machine itself; moreover, the vibration frequencies of the rotating machine can cause resonance to delicate parts of the nacelle.
Other applications that require the damping of the vibrations comprise for example industrial rotating machines and tools with rotating parts.
Damping systems of mechanical type for vibrations are known, for example constituted by masses eccentrically positioned on one or more rotating parts of the rotating machine, so that to generate in turn forces as much equivalent and opposite as possible for drastically reducing the vibrations of the machine itself.
However, said systems are not efficient and can be only empirically and not in series optimized. Namely, the working tolerances of the parts of the rotating machine, as well as other constructive differences, that are inevitably present during the production in series more or less extended on the rotating machines, cause to have rotating machines that vibrate in a slightly different way one from another.
Furthermore, said masses inevitably contribute to the weight increase of the rotating machine upon which they are installed, and this can be unacceptable for determined application fields.
Said masses, if not correctly fixed to the rotating part, can be subjected to detachment or movement events with the serious risk of increasing the vibrating behavior of the machine upon which they are mounted.
Systems of active vibration damping of a rotating machine that use electro-mechanic technologies are known. Said systems are rather complex and typically require supplying systems and electronic control systems outside the rotating machine itself.
There are particular applications of rotating machines, that include in a non restrictive way, also the aeronaval field, wherein the transfer of the control system of the active vibration damping system is complex, extremely expensive and dangerous.
For example, bringing said control system from an aircraft engine to the interior of a nacelle, on the aircraft wing or even only outside the engine but still within the nacelle that encloses it, is heavy in terms of weight (because of the copper conductors that must go at least in a straight way along the whole wing of the aircraft and must be redundant for security reasons), as well as dangerous (a long conductor can damage itself, ground part of the electric signal, cause short-circuits and fires).
Furthermore, the existing regulations impose limiting restraints related to the electromagnetic emissions of the circuit on the surrounding environment. In fact, as it is known, the navigational instrumentation is particularly sensitive to the radio interferences caused by spurious electromagnetic emissions of electronic circuits, and the risk of interference on the normal functioning of the navigational instrumentation is absolutely unacceptable in terms of security.
Moreover, said types of control systems are subjected to the risk of electric blackout. For example, in case of even only a temporary lack of power supply, an electronic control system of a complex type does not work anymore and it often requires a rather long resetting (particularly if it is complex and is partially controlled by means of a dedicated software platform, this case being called reboot) that is unacceptable in critical applications such as the aeronautical industry.